Adding basement washroom

Hello,
I want to add a basement washroom to my home. I would like to include a toilet, shower and lav. I would like to wet vet the group. I know that typically the wet vent runs up through the lav but I have no wall to hide the vertical vent pipe as the lav will be facing a granite stone foundation wall. I would like to wet vent the lav and toilet through the shower drain. Would this be acceptable? I live in Ontario Canada.

I doubt it would be acceptable or work right, but then I'm neither a pro nor up on Canadian codes. Also, lots of people think of the drain from above as a vent - it is not. Once a pipe is used as a drain, it is always a drain. To vent this group, you'd need to run a pipe up above the existing fixtures that drain into the pipe and into their vent. This is at least 42" above the floor of the highest drain or 6" above the highest fixture drain, whichever is higher. Or, you can vent it through the roof on its own.

I cannot speak for Canada, but the reason that wet venting through the lav is accepted here is because a lavatory only puts out a small volume of water (rated at 1 dfu(drainage fixture unit)), and then then drain/vent pipe is over-sized to 2" enabling a "safe" wet vent. Because all of the other fixtures have a higher dfu rating, it is not allowed to wet vent through them.

You will need to explore your design options by adding a wall or chase for the vent(s), or leave them exposed. As a DIY project, it is sometimes easier to change the layout to make the plumbing more simple. Plumber's don't get this option.

For me to get a plumbing permit, I have to provide an isometric drawing of the planned drainage system to our building department which has to be approved. Then when the work is done, the building inspector comes to verify that the installation meets our plumbing code. I mention this because it is good practice to plan out your project on paper, and isometric works good for plumbing. This also enables you to build a valid materials list for the project from the start, as all your fittings and sizes should be marked on the drawing.

If you are planning on putting the p-trap in the floor, that would be an S trap. Not legal.
The only way wet venting works, is with a fixture that is truly vented. Expecting a shower drain to vent a lav? Nope!
The lav is the one in this case is the one that needs to vent the other fixtures. I'm afraid you have it backwards.

quote; I would like to wet vent the lav and toilet through the shower drain. Would this be acceptable? I live in Ontario Canada.

There is no way you can "wet vent" a legal lav drain through ANY shower connection. You would have to mount the shower floor at least 24" above the room's floor, and even then it would be an illegal, "major over a minor" situation.